Suppression of college at one time associated with mental disorder (11)
I believe the answer is:
concealment
'suppression' is the definition.
(suppress can mean to conceal or hide)
'college at one time associated with mental disorder' is the wordplay.
'college' becomes 'c'.
'at one time' becomes 'once' (both can mean 'in the past').
'associated with' is a charade indicator (letters next to each other).
'disorder' is an anagram indicator (a disordered version of the letters).
'mental' anagrammed gives 'alment'.
'c'+'once'+'alment'='CONCEALMENT'
'of' acts as a link.
(Other definitions for concealment that I've seen before include "Act of hiding" , "Process of hiding" , "Hiding; secrecy" , "Whitewash" .)